1. Field of the Invention
The present invention relates to a plasma processing apparatus and, more particularly, to a plasma processing apparatus using a microwave for generating plasma in a process chamber.
2. Description of the Related Art
Recently, in a semiconductor device manufacturing process, plasma processing apparatuses have been used to perform semiconductor producing processes such as a deposition process, an etching process or an ashing or stripping process since high-density integration and fine structure are required for semiconductor devices. Particularly, a microwave plasma processing apparatus has become popular since the microwave plasma processing apparatus is capable of generating stable plasma at a relatively low vacuum of 0.1 millitorr (mTorr) to several tens of mTorr. The microwave plasma processing apparatus generates high-density plasma by using a microwave or a combination of a microwave and a magnetic field generated by a ring-like coil.
In a typical microwave plasma processing apparatus, a 2.45 GHz microwave is introduced into a process chamber via a waveguide, a transmission window and a slot electrode, in that order. A reaction gas is also introduced into the process chamber, which is maintained at a predetermined negative pressure. The reaction gas introduced into the process chamber is changed into active radicals and ions by the microwave so as to produce plasma. An object to be processed such as a semiconductor wafer is placed in the process chamber so that a predetermined process such as an etching process is Performed on the object by utilizing action of the plasma.
The microwave may be passed through a wavelength reducing member made of a dielectric material before entering the slot electrode so that the wavelength of the microwave introduced into the process chamber is reduced or shortened. The wavelength reducing member is used to make it possible to use a reduces distance between adjacent slits formed in the slot electrode. A typical wavelength reducing member is disclosed in Japanese Laid-open Patent Application No. 9-63793.
The transmission window, which is formed of quartz or alumina, may deteriorate due to heat associated with plasma. The wavelength reducing member and the slot electrode are subjected to thermal expansion by the heat of the plasma. If the slot electrode, which is made of, for example, a copper plate, changes in its length due to thermal expansion, the length of each slit provided in the slot electrode is undesirably changed. This may cause a decrease in the plasma density or localization (unevenness) of the plasma in the process chamber.
The decrease in the plasma density may slow down a plasma processing speed such as an etching rate or a film deposition rate. As a result, if the plasma processing is controlled based on a processing time, there may be a case in which a desired result of the plasma processing (such as a depth by plasma etching or a thickness by plasma deposition performed on the semiconductor wafer) cannot be obtained when the plasma processing is applied for a predetermined time period. Additionally, if the plasma density in the process chamber is localized, the magnitude of the result of plasma processing may vary locally or be uneven on the semiconductor wafer.
In order to solve the above-mentioned problems, Japanese Laid-Open Patent Application No. 3-191073 discloses a microwave plasma processing apparatus having a cooling device to cool the transmission window using cooling water. Additionally, the above-mentioned Japanese Laid-Open Patent Application No. 9-63793 discloses a cooling jacket provided to a cover of the wavelength reducing member and the slot electrode.
However, Japanese Laid-Open Patent Application No. 9-63793 does not disclose a material usable for the wavelength reducing member. If an appropriate material is not selected for the wavelength reducing member, preferable heat transmission cannot be achieved. This may cause a problem in that a precise temperature control cannot be performed, and uniformity of plasma processing cannot be obtained.
Additionally, there are other component parts which do not have a good heat resistance, such as an O-ring provided between the process chamber and the wavelength reducing member. Accordingly, a temperature of such component parts must be maintained below a predetermined temperature so as to eliminate the influence of the heat associated with plasma.
On the other hand, in a plasma CVD apparatus which is one of the plasma processing apparatuses, it is preferable that a temperature inside the process chamber be maintained as high as possible so as to eliminate influence of water existing in the process chamber. That is, if water exists in the process chamber in the form of liquid or mist, the water may enter a film produced on a semiconductor wafer by the plasma processing. Accordingly, if a cooling device is provided to the process chamber without consideration of such a problem regarding water, the quality of plasma processing may be reduced.
As mentioned above, the conventional plasma processing apparatuses cannot eliminate undesirable influence of the heat associated with plasma while maintaining the quality of an object to be processed.
It is a general object of the present invention to provide an improved and useful microwave plasma processing apparatus in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a microwave plasma processing apparatus which can prevent the component parts of the process chamber from being influenced by heat associated with plasma, thereby improving the quality of plasma processing performed in the process chamber.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a microwave plasma processing apparatus comprising: a wavelength reducing member reducing a wavelength of a microwave transmitted therethrough: a slot electrode guiding the microwave exiting the wavelength reducing member, the slot electrode provided adjacent to the wavelength reducing member; a first temperature control device controlling a temperature of at least one of the slot electrode and component parts including the wavelength reducing member provided in the vicinity of the slot electrode; and a process chamber into which the microwave exiting the slot electrode is introduced so that plasma is generated by the microwave within the process chamber.
According to the present invention, the temperature of the slot electrode is controlled by controlling the temperature of a component part adjacent to the slot electrode by utilizing transmission of heat between the slot electrode and the component parts such as the wavelength reducing member. That is, the temperature of the slot electrode can be maintained at a predetermined desired temperature. Thus, a length of each slit formed in the slot electrode can be maintained at a predetermined length, thereby generating plasma having a uniform density within the process chamber.
The microwave plasma processing apparatus may include a dielectric material member provided between the slot electrode and the process chamber, and the first temperature control device controls the temperature of the dielectric material member instead of the temperature of the wavelength reducing member so as to control the temperature of the slot electrode.
Additionally, there is provided according to another aspect of the present invention a plasma processing method comprising the steps of: placing an object to be processed in a process chamber; controlling a pressure inside the process chamber; controlling a temperature of a slot electrode radiating a microwave toward the process chamber by utilizing transmission of heat between the slot electrode and other component parts surrounding the slot electrode; introducing a reaction gas into the process chamber; supplying a microwave to the slot electrode; and-processing the object by plasma of the reaction gas generated by the microwave introduced into the process chamber.
According to this invention, the temperature of the slot electrode radiating a microwave toward the process chamber is controlled by utilizing transmission of heat between the slot electrode and component parts surrounding the slot electrode. That is, the temperature of the slot electrode can be maintained at a predetermined desired temperature. Thus, a length of each slit formed in the slot electrode can be maintained at a predetermined length, thereby generating plasma having a uniform density within the process chamber.
Additionally, according to another aspect of the present invention a plasma processing method comprising: placing an object to be processed in a process chamber; controlling a pressure inside the process chamber; controlling a temperature of a slot electrode radiating a microwave toward the process chamber; introducing a reaction gas into the process chamber; supplying a microwave to the slot electrode when a temperature of the slot electrode is below a predetermined temperature; and processing the object by plasma of the reaction gas generated by the microwave introduced into the process chamber.
According to the present invention, a microwave is supplied to the slot electrode when the temperature of the slot electrode is below a predetermined temperature. That is, the temperature of the slot electrode increases due to the microwave transmitted therethrough, and the microwave is supplied when the slot electrode has reached a temperature which is a predetermined temperature below the temperature to be achieved when the plasma processing is being performed. This can eliminate over heating the slot electrode due to the heat generated by transmission of the plasma through the slot electrode.